Photographic developers



Patented July 5, l938 UNITED sTATEs 2,122,599 7 PHOTOGRAPHIC DEVELOPERSGustav Wilmanns, Wolfen (Kreis Bitterfeld) and Wilhelm Schneider, Dessau(Anhalt) Germany, assignors to Agfa Ansco Corporation, Binghamton, N.Y., a corporation of New York Nb Drawing. Application December 16, 1936,Serial No. 116,236. In Germany December 23,

16 Claims. (o1. 95-8) 7 The present invention relates to photographicdevelopers. 4

One of its objects is a developer for photographic silver halideemulsions by which the 5 silver halide is transformed into silver.Without previous exposure. Another object is a photographic developerfor the reversal process. Further objects willbe seen from the detailedspecification following hereafter.

For many purposes, for instance for reversal development, it is oftendesirable that the second development should be possible withoutprevious exposure to light; for example, when the film has beendeveloped in a bath it is troublesome to 15 have to remove the wet filmfrom the bath, ex-

pose it to light and return it to the bath. It has been proposed toavoid this exposure by using as an equivalent expedient certain reducingsubstance, for instance hydrosulfite, thiosinamine or 20 the like. Suchreducing agents, however, are generally of very low stability and cannotbe preserved; in addition theyhave other disadvantages', for instance adisagreeable odour.

The present invention relates to a method for avoiding the foregoingdifllculties by using a new namely developers which contain in'themolecule an atom grouping COCHOH or in tautomeric form COH=COH. Thisatom 30 grouping may be in an open chain or in a heterocyclic nucleus.Such substances are, for example benzoin which may contain varioussubstituents in the nucleus, dioxindols, 2,3 dihydroxythionaphthenes.These substances'may be used either 35 alone or in admixture with normaldevelopers.

. The mixed developers have the property of developing first smallsilver nuclei which then, after this initial development, are furtherdeveloped by the normal developer.

40 The following are examples of suitable developers:

I. Dioxindol grams 2 Su1flte -do 10 45 Potassium carbonate do 6 Water cc200 II. Benzoin sulfonic acid grams' 2 Sulflte do 10 Sodium hydroxide do0.6 Water cc 200 III. Dioxindol grams 2' Hydroquinone do 10 Sulfite do50 Potassium carbonate do 30 55 Water "cc 1000 IV. 2,3dihydroxythionaphthene v c rams 2 Sulflte h do 10 Potassium carbonate do6 60 Water cc..'

group of developers for the purpose in question,

When an unexposed film is developed in any of these developers there isproduced in -10 minutes of developing period. a complete blackening.

What we claim is: 1. In a process of producing reversal images inexposed silver halide emulsions the step which \comprises carrying outthe second development without exposure between first and seconddevelopment by means of a developing bath the active component of whichis formed bya compound selected from the group consisting of benzoines,dioxindoles and 2,3 dihydroxythionaphthenes.

2. In a process of producing reversal images in exposed silver halideemulsions the step which comprises carrying out the second developmentwithout exposure between the first and second development by means of anordinary developing bath containing'a compound selected from the groupconsisting of benzoins, dioxindoles and 2,3 dihydroxythionaphthenes. I

3. In a process of producing reversal images in exposed silver halideemulsions the step which comprises carrying out the second developmentwithout exposure between first and second development by means of a.developing bath comprising a'dioxindol.

' 4. In a process of producing reversal images in exposed silver halideemulsions the step which comprises carrying out the second developmentwithout exposure between first and second development by means of adeveloping .bath comprising a 2,3 dihydro'xythionaphthene.

5. In a process of producing reversal images in exposed silver halideemulsions the step which 7 comprises carrying out the second developmentwithout exposure between first and second de-,- velopment by means of adeveloping bath comprising a substituted benzoin.

6. In a process of producing reversal images in exposed silver halideemulsions the step which comprises carrying out the second developmentwithout exposure between first and second development by means of a"developing bath having the following composition:

Dioxindol "grams" 2 sulfite I. do 10 Potassium carbonate do 6 Water cc200 2,3 dihydroxythionaphthene grams 2 Sulfite do 10 Potassium car do 6water or 200 In a' process of producing reversal images in 6 opment bymeans of a developing bath having the following composition:

Benzoin sulfonlc acid grams 2 Bulnte do 10 10 Sodium hydroxide do 0.6Water 200 9. A photographic, developing bath for silver halide emulsionscomprising a compound selected from the group consisting of benzoins,dioxindoles and 2,3 dihydroxythionaphthenes.

'10. A photographic developing bath for silver halide emulsions havingas the active component a compound selected from the group consisting ofbenzoins, dioxindoles and 2,3 dihydroxythlonaphthenea.

11. A photographic developing bath for silver halide emulsionscomprising a dioxindol.

12. "A photographic developing bath for silver halide emulsionscomprising a 2,3 dihydroxythionaphthene'.

13. A photographic developing bath for silver halide emulsionscomprising a substituted benzoin.

14. A photographic developing bath for silver halide emulsions havingthe following composition: v

Dioxin n rams" 2 Sulflte do 10 Potassium carbonate do 6 Water- 200 15. Aphotographic developing bath-forsilver halide emulsions having thefollowing composition:

2,3-dihydroxythionaphthene grams 2 Sulflte -:lo 10 Potassium carbonatedo 6 Water 200 16. A photographic developing bath for silver halideemulsions having the following composition:

Benzoin sulfonic acid grams 2 Sodium hydroxide dn 0,

Water 200 GUSTAV WILMANNS.

WILHELM SCHNEIDER.

